Activity enhancement of high silica zeolites

ABSTRACT

A crystalline high silica-containing zeolite such as ZSM-5 is treated with an ammoniacal alkali metal aluminate so as to enhance the catalytic activity thereof.

CROSS REFERENCE TO RELATED CASES

This application is related to U.S. patent application Ser. No. 288,604,filed July 30, 1981 and now abandoned, entitled ACTIVITY ENHANCEMENT OFHIGH SILICA ZEOLITES of Pocken Chu.

BACKGROUND OF THE INVENTION

This invention relates to a method of enhancing the activity of highsilica-containing crystalline materials by a process which involvescontacting them with ammoniacal alkali metal aluminate solutions so asto cause the aluminium in the solution to become associated with thehigh silica-containing crystalline material and to enhance its activity.

High silica-containing zeolites are well known in the art and it isgenerally accepted that the ion exchange capacity of a crystallinealuminosilicate is directly dependent upon its aluminum content. Thus,for example, the more aluminum there is in a crystalline structure, themore cations are required to balance the electronegativity thereof, andwhen such cations are of the acidic type such as hydrogen, they imparttremendous catalytic activity to the crystalline material. On the otherhand, high silica-containing zeolites having little or substantially noaluminum have many important properties and characteristics and a highdegree of structural stability such that they have become candidates foruse in various processes including catalytic processes. Materials ofthis type are known in the art and include high silica-containingaluminosilicates such as ZSM-5 (U.S. Pat. No. 3,702,886), ZSM-11 (U.S.Pat. No. 3,709,979), and zeolite ZSM-12 (U.S. Pat. No. 3,832,449) tomention a few.

The silica-to-alumina ratio of a given zeolite is often variable; forexample, zeolite X can be synthesized with silica-to-alumina ratio offrom 2 to 3; zeolite Y from 3 to about 6. In some zeolites, the upperlimit of silica-to-alumina ratio was unbounded. ZSM-5 is one suchexample wherein the silica-to-alumina ratio is at least 5. U.S. Pat. No.3,941,871 discloses a crystalline metal organosilicate essentially freeof aluminum and exhibiting an x-ray diffraction pattern characteristicof ZSM-5 type aluminosilicates. U.S. Pat. Nos. 4,061,724; 4,073,865; and4,104,294 describe microporous crystalline silicas or organosilicateswherein the aluminum content present is at impurity levels.

Because of the extremely low aluminum content of these silica-containingzeolites, their ion exchange capacity is not as great as materials witha higher aluminum content. Therefore, when these materials are contactedwith an acidic solution and thereafter are processed in a conventionalmanner, they are not as catalytically active as their higheraluminum-containing counterparts.

The novel process of this invention permits the preparation of highsilica-containing materials which have all the desirable propertiesinherently possessed by such high silica materials and, yet, have anacid activity which heretofore has only been possible to be achieved bymaterials having a higher aluminum content.

DESCRIPTION OF THE PRIOR ART

It is to be immediately understood that there are many patents andtechnical articles relating to contacting crystalline aluminosilicatezeolites as well as high silica-containing materials havingsubstantially no aluminum with solutions of aluminum ions in order tobase exchange the aluminum for the cations originally associated withthe crystalline materials. Additionally, there are many patents andtechnical articles wherein a high silica zeolite is incorporated into amatrix or binder wherein such processing also involves contacting saidcrystalline material with aluminum ions. Typical patents concerned withthe above techniques would include some of the patents alreadymentioned, i.e. ZSM-5, ZSM-12, ZSM-11, as well as U.S. Pat. Nos.3,140,329; 3,629,152; 3,429,830; 3,562,148; 3,582,497; 3,410,808;3,403,110, merely to mention a few. The novel process of this inventionis not concerned with an improved process for incorporating acrystalline material in a matrix nor is it concerned with a simple ionexchange process, but rather, it is concerned with a noval process forenhancing the acid activity of a crystalline material. In the prior art,previously referred to, there is no teaching of treatment of acrystalline material with an ammoniacal alkali metal aluminate solutionin order to enhance the activity of a crystalline material.

In a copending application entitled ACTIVITY ENHANCEMENT OF HIGH SILICAZEOLITES of Pochen Chu, filed July 30, 1981, Ser. No. 288,604, there isdisclosed and claimed a process for enhancing the activity of highsilica zeolites by contacting them with a solution containing both analkali metal aluminate and a quaternary ammonium compound at a pH of atleast 7 and most preferably 9-12. This invention represents animprovement in that expensive quaternary ammonium compounds are notneeded and the procedure involves the use of common and relativelycheaper materials.

DESCRIPTION OF PREFERRED EMBODIMENTS

As has heretofore been stated, the novel process of this invention isconcerned with the treatment of high silica containing crystallinematerial. The expression "high silica-containing crystalline material"is intended to define a crystalline structure which has asilica-to-alumina ratio greater than 500 and more preferably greaterthan 1000 up to and including those highly siliceous materials where thesilica-to-alumina ratio is infinity or as reasonably close to infinityas practically possible. This latter group of highly siliceous materialsis exemplified by U.S. Pat. Nos. 3,941,871; 4,061,724; 4,073,865;4,104,294 wherein the materials are prepared from reaction solutionswhich involve no deliberate addition of aluminum. However, tracequantities of aluminum are usually present due to the impurity of thereaction solutions. It is to be understood that the expression "highsilica-containing crystalline material" also specifically includes thosematerials which have other metals besides silica and/or aluminaassociated therewith, such as boron, iron and chromium, etc. Thus, theonly requirement with regard to the starting materials utilized in anovel process of this invention, is that they have a silica-to-aluminaratio greater than about 500, irrespective of what other materials ormetals are present in the crystal structure. The particularly preferredstarting materials for the novel process of this invention are thosecrystalline materials which have an x-ray diffraction patterncharacteristic of ZSM-5, ZSM-11, and ZSM-12 irrespective of theirchemical composition other than the minimum silica-to-alumina ratio. Thepreferred starting material for the novel process of this invention is ahigh silica-containing ZSM-5.

The novel process of this invention is simple in nature and easy tocarry out, although the results obtained therefrom are dramatic. Thenovel process of this invention is carried out simply by contacting ahigh silica-containing zeolite either as crystallized or aftercalcination with an ammoniacal alkali metal aluminate solution,preferably an ammoniacal sodium aluminate solution, at a pH of about 8to 14 and, more preferably, a pH greater than 10. A particularlypreferred technique involved contacting said high silica zeolite withsaid ammoniacal alkali metal aluminate solution by vacuum impregnationtechniques.

The amount of solution utilized to treat the high silica-containingzeolites is not narrowly critical and the solution to zeolite ratio canvary from 0.3 to >10 grams of solution per gram of zeolite. The amountof solution will vary as a function of its concentration and the desiredenhancement of activity.

The process is carried out by treating said high silica zeolite ascrystallized or after calcination with the above described solution attemperatures ranging from 20° to 50° C. and preferably from 20° to 35°C. for periods of time ranging from 20 minutes to 30 days; preferablyfrom 1/2 hour to 5 days.

Following the above treatment, the high silica-containing zeolite isprocessed into its catalytically active form by conventional techniques,such as base exchange with appropriate cations such as hydrogen,ammonium, rare earth, and mixtures thereof. The high silica-containingmaterials are then calcined by heating to a temperature in the range of200°-600° C. in an atmosphere such as air, nitrogen, etc. andatmospheric, subatmospheric, or superatmospheric pressures for betweenabout 1 and 48 hours. It is to be understood that the highsilica-containing zeolites can, if desired, be incorporated in a matrixby techniques well known in the art. Conventional matrices includeinorganic oxides, such as silica, alumina, silica alumina, etc. Thefollowing examples will illustrate the novel process of this invention.

EXAMPLE 1

A 2-g. sample of ZSM-5 zeolite having a silica-to-alumina ratio of about26,000 and a sodium content of about 0.23 weight percent was impregnatedwith 3 grams of 5 weight percent sodium aluminate solution and calcinedin air at 538° C. for 20 hours.

EXAMPLE 2

The product of Example 1 was treated with a 1-N 8 weight percentsolution of ammonium nitrate.

EXAMPLE 3

A sample of the same ZSM-5 used above was vacuum impregnated with asolution of sodium aluminate which was diluted by an equal volume ofconcentrated (12N) NH₄ OH. The pH was 12.4. After 30 minutes, the samplewas dried and submitted to three cycles of 1N NH₄ NO₃ treatment followedby hot water washing. The sample was dried and calcined at 538° C. priorto testing.

The products of Examples 1-3 were evaluated for alpha activity.

As is well known in the art, the alpha value gives an approximateindication of the catalytic cracking activity of the catalyst comparedto a standard catalyst, and it is the relative rate constant of normalhexane conversion per unit volume of oxides per unit time. It is basedon the activity of highly active silica-alumina cracking catalysts takenas an alpha of 1, and this test is described in U.S. Pat. No. 3,354,078and the Journal of Catalysis, Vol. 4, pp. 522-529, Aug. 1965.

The results are shown in the following table:

                  TABLE 1                                                         ______________________________________                                        Activity of High SiO.sub.2 ZSM-5 After Treatment                              Example                     Alpha                                             ______________________________________                                        1           NaAlO.sub.2 treat                                                                             0.4                                               2           NaAlO.sub.2 /NH.sub.4 NO.sub.3 treat                                                          0.2                                               3           NaAlO.sub.2 /NH.sub.4 OH imp +                                                                12                                                            NH.sub.4 NO.sub.3 treat                                           ______________________________________                                    

From the above table, it can be seen that the noval process of thisinvention resulted in a dramatic increase of activity. The procedure ofExamples 1 and 2 did not result in any significant improvement, whereasthe process of this invention (Example 3) did enhance activity.

What is claimed is:
 1. A method for enhancing the activity of a highsilica-containing crystalline zeolite having a silica-to-alumina ratiogreater than 500 which comprises contacting said material with anammoniacal solution of an alkali metal aluminate for a period of timeranging from 1/2 hour to 5 days at a temperature of from 20° to 50° C.and at a pH of at least
 10. 2. The process of claim 1 wherein the alkalimetal aluminate is sodium aluminate.
 3. A method of enhancing theactivity of a high silica zeolite of the ZSM-5 type having asilica-to-alumina ratio of at least 500 which comprises contacting saidzeolite with an ammoniacal solution of an alkali metal aluminate at atemperature of from 20° to 50° C., for a period of time ranging from 1/2day to 5 days and at a pH of at least
 10. 4. The process of claim 3wherein the alkali metal aluminate is sodium aluminate.
 5. The processof claim 4 wherein the ZSM-5 zeolite has a silica-to-alumina ratio inexcess of
 500. 6. The process of claim 4 wherein the ZSM-5 zeolite has asilica-to-alumina ration in excess of
 1600. 7. The process of claim 4wherein the ZSM-5 zeolite has a silica-to-alumina ratio approachinginfinity.
 8. The process of claim 3 wherein the ammoniacal alkali metalaluminate is applied by vacuum impregnation.